This invention pertains to a special gravimetric measurement of the percent of high boiling point hydrocarbons in a way that the measurement is related to and useful in chromatographic analysis of the same hydrocarbon. More particularly, the measurement uses inert gas sweep and similar temperatures, thereby allowing direct correlation of results.
The American Society for Testing and Materials has a "Standard Test Method for BOILING RANGE DISTRIBUTION OF PETROLEUM FRACTIONS BY GAS CHROMATOGRAPHY", ANSI/ASTM D 2887-73, published October 1973, pages 789-797. This test method covers determinations of the boiling range distribution of petroleum products whose final boiling point is 1000.degree. F. (538.degree. C.) or less at atmospheric pressure. The same ASTM manual at pages 716-722 sets forth a "Proposed Test Method for BOILING RANGE DISTRIBUTION OF CRUDE PETROLEUM BY GAS CHROMATOGRAPHY", published November 1976. This proposed test has no status as an ASTM standard and covers crude petroleum with high-boiling fractions. In the procedure a sample of the unknown petroleum is injected with a micro syringe and the temperature of the test sample raised at a reproducible rate while the sample is being swept with an inert carrier gas. The type gas depends on the type of detector. For thermal conductivity detectors, helium or hydrogen is used. For flame ionization detectors, nitrogen, helium or argon is used. The area under a chromatogram is recorded with time and compared to the chromatogram of a known calibrated paraffinic hydrocarbon mixture. An internal standard of at least four paraffinic hydrocarbons, preferably above C.sub.14 is also used. The chromatographic procedure raises the sample to a predetermined equipment temperature which is equated to a much higher maximum test boiling point temperature, e.g. 1000.degree. F. When the hydrocarbon sample has components which do not vaporize or are not segregated by the chromatograph, it is necessary to estimate the percentage of the higher boiling point hydrocarbons by comparing the areas under known and unknown chromatograms. Chromatographic analyses are time consuming. The calculation is subject to significant error both in sample handling and injection and in equipment operation. It would, therefore, be useful to have a simple procedure for checking the higher boiling fraction. Ordinary, gravimetric techniques are not suitable for this purpose because of carbonization, splattering, and other similar problems. Moreover, standard gravimetric techniques are not related to the chromatographic technique where the sample is not actually raised to the boiling point temperature of the hydrocarbon being measured at any given moment.